1. Field of the Invention
The present invention relates generally to packages for optical waveguide fiber devices, and particularly to temperature-compensated optical devices.
2. Technical Background
One important consideration in optical communication systems is the ability of the optical communication system to operate reliably over a temperature range of about 0xc2x0 C. to about 70xc2x0 C. Reliability across this temperature range is difficult to achieve because the optical properties of many components used in optical communication systems vary with temperature.
Fiber Bragg gratings are widely used in optical communication systems. Fiber Bragg gratings are optical waveguide fiber devices that may be used to selectively reflect specific wavelengths of light propagating in an optical waveguide fiber. Fiber Bragg gratings consists of an array of shifts in the index of refraction along the path of light propagation in the optical fiber. The periodicity of the grating determines the wavelengths that are reflected by the fiber Bragg grating. A shift in the periodicity of the grating of 1 xcexcm results in a shift in the reflected wavelength of 50 picometers.
Several approaches have been proposed to compensate for changes in ambient temperature. Many approaches are based upon placing the fiber Bragg grating in tension and then regulating the amount of tension to compensate for changes in the temperature of the fiber Bragg grating.
One specific approach to temperature compensation is to stake the fiber to a negative expansion substrate material, such as xcex2-eucryptite. As the temperature increases, the substrate contracts thereby maintaining the reflective wavelength of the grating. This approach suffers from the fact that xcex2-eucryptite material requires a hermetic packaging in order to function reliably over the range of environmental conditions specified for optical communication systems. This approach has proven to be difficult and costly. Furthermore, the overall size of the hermetically sealed negative expansion substrate package is large, in a relative sense. As optical communication systems develop the movement has been towards smaller packages and the placement of more components into the same or smaller volume.
Another approach uses materials of dissimilar thermal expansion characteristics to form a substrate to which the fiber is attached. Because of the differences in thermal expansion of the two dissimilar materials as temperature increases, the distance between the two attachment points of the fiber Bragg grating contracts. The amount of contraction depends on the choice of materials and the actual dimensions of the substrate. Any optical component package must pass stringent environmental and shock/vibration testing. The choice of material and the mass and size of a component are important considerations. For example, an optical component package having a large mass may require special additional packaging to stand vibration testing. Specialized packaging adds to the cost and size of the overall product.
For example, a tubular embodiment of such a package was presented in Applied Optics Volume 34, No. 30, Oct. 28, 1995. The article stated that the package must be a minimum of 40% longer than the grating itself. In this embodiment the fiber must be attached to each of the two dissimilar metals, possibly requiring two different attachment techniques. The assembly fold-over nature of the package, as it is presented, also precludes the simple attachment of the device to the fiber. The actual device disclosed in the article required an intermediate attachment to facilitate assembly. This intermediate attachment took the form of a threaded structure, which added cost and complexity to the package.
One aspect of the present invention is a package for temperature compensating a Bragg grating region of an optical waveguide fiber including a first tubular member attached to the optical waveguide fiber. The first tubular member is attached to the optical waveguide fiber and has a first coefficient of thermal expansion. The package further includes a second tubular member coupled to the first tubular member. The second tubular member has a coefficient of thermal expansion greater than the first coefficient of thermal expansion. The package also includes a third tubular member coupled to the second tubular member and to the optical waveguide fiber. The third tubular member has a coefficient of thermal expansion equal to the first coefficient of thermal expansion. The package encapsulates the Bragg grating region of the optical fiber.
In another aspect, the present invention includes a package for temperature compensating a fiber Bragg grating of an optical waveguide fiber including a first tubular member having a first coefficient of thermal expansion. The package further includes a second tubular member coupled to the first tubular member, the second tubular member having a second coefficient of thermal expansion. The package also includes a third tubular member coupled to the second tubular member, the third tubular member having a third coefficient of thermal expansion. The first tubular member, the second tubular member and the third tubular member define a cavity having a first end and a second end and the fiber Bragg grating is disposed within the cavity. The optical waveguide fiber is coupled to the first end and the second end.
In another aspect, the present invention includes a package for temperature compensating a fiber Bragg grating of an optical waveguide fiber including a first tubular member having a first coefficient of thermal expansion. The first tubular member includes a first end coupled to the optical waveguide fiber and a second end. The package further includes a second tubular member having a second coefficient of thermal expansion. The second tubular member includes a third end coupled to the second end and a fourth end. The package also includes a third tubular member having a third coefficient of thermal expansion. The third tubular member includes a fifth end coupled to the fourth end and a sixth end. The package also includes a cap, coupled to said optical waveguide fiber, engageable with the sixth end. The fiber Bragg grating is disposed between said first end and said cap and the first coefficient of thermal expansion and the third coefficient of thermal expansion are substantially the same.
In another aspect, the present invention includes a method for forming an optical waveguide device. The method includes the step of providing a first member having an inner wall and defining a first cavity having a first predetermined diameter. The method further includes the step of providing a second member having an inner wall defining a second cavity having a second predetermined diameter, wherein the second member is slidably engageable with the first cavity. The method further includes the step of inserting the second member into the first cavity. The method further includes the step of coupling the first member to the second member. The method also includes the step of providing a third member having an inner wall defining a third cavity having a third predetermined diameter, wherein said third member is slidably engageable with said cavity. The method further includes the step of inserting the third member into the second cavity and coupling the second member to the third member. The method further includes the step of providing an optical waveguide fiber of a second predetermined diameter less than the third predetermined diameter. The method further includes the step of inserting said optical waveguide fiber into said third cavity. The method also includes the steps of coupling said optical waveguide fiber to said first member; and coupling said optical waveguide fiber to said third member.
One advantage of the present invention is that it allows for a reduction in size over typical temperature compensated fiber Bragg grating packages.
Another advantage of the present invention is that only a single method is required to attach the optical waveguide fiber to the package at two spaced apart locations.
Another advantage of the present invention is that it is less complicated than currently known methods of temperature compensating optical fiber devices.
Another advantage of the present invention is that the relative lack of complexity of the individual elements that are incorporated into different embodiments of the invention have the potential to significantly lower the cost of manufacture compared to currently known methods.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.